Significant progress has been made realising telecom quantum optical memories across different material platforms. Atomic-based systems require an optical transition in the telecom range, with cryogenically-cooled trivalent erbium ions in solid-state hosts a popular choice [1]}. Protocols including the Atomic Frequency Comb (AFC) [2]}, [3]}, [4]}, stark-modulated AFC [5]}, [6]}, controlled-reversible inhomogeneous broadening [7]} and revival of silenced echo [8]} have been performed in erbium doped Y\(_2\) SiO\(_5\) , which include realisations in nano-photonic structures [3]}, [5]}. Other hosts have been explored, with demonstrations of AFC in erbium-doped optical fiber [11]}, [12]} and lithium niobate waveguides [13]}. Further, frequency conversion via non-linear processes have been used to interface telecom light with quantum memories, including four-wave mixing in cold atomic clouds [14]}, [15]} and non-linear crystals [16]}, [17]}. Furthermore, opto-mechanical interactions have enabled telecom light storage in optical fiber [18]}, chalcogenide glass chips [19]} and in nanofabricated mechanical resonators [20]}.
